The nomenclature of monoclonal antibodies is a naming scheme for assigning generic, or nonproprietary, names to monoclonal antibodies. An antibody is a protein that is produced in B cells and used by the immune system of humans and other vertebrate animals to identify a specific foreign object like a bacterium or a virus. Monoclonal antibodies are those that were produced in identical cells, often artificially, and so share the same target object. They have a wide range of applications including medical uses. This naming scheme is used for both the World Health Organization's International Nonproprietary Names (INN) and the United States Adopted Names (USAN) for pharmaceuticals. In general, word stems are used to identify classes of drugs, in most cases placed word-finally. All monoclonal antibody names assigned until 2021 end with the stem -mab; newer names have different stems. Unlike most other pharmaceuticals, monoclonal antibody nomenclature uses different preceding word parts (morphemes) depending on structure and function. These are officially called substems and sometimes erroneously infixes, even by the USAN Council itself. The scheme has been revised several times: in 2009, in 2017, in 2021, and in 2022. Components Stem Until 2021, the stem -mab was used for all monoclonal antibodies as well as for their fragments, as long as at least one variable domain (the domain that contains the target binding structure) was included. This is the case for antigen-binding fragments and single-chain variable fragments, among other artificial proteins. The new scheme, published in November 2021, divides antibodies into four groups: Group 1 uses the stem -tug for full-length unmodified immunoglobulins, those that might occur as such in the immune system. Group 2 has the stem -bart for full-length antibodies artificial, which contain one or more engineered regions (at least one point mutation). Group 3 uses -mig for multi-immunoglobulins of any length, comprising bispecific and multispecific monoclonal antibodies. Finally, group 4 assigns the stem -ment for monospecific antibody fragments without an Fc region. Other antibody parts (such as Fc regions) and antibody mimetics use different naming schemes. Substem for source For antibodies named until early 2017, the substem preceding the stem denotes the animal from which the antibody was obtained. The first monoclonal antibodies were produced in mice (substem -o-, yielding the ending -omab; usually Mus musculus, the house mouse) or other non-human organisms. Neither INN nor USAN has ever been requested for antibodies from rats (theoretically -a-), hamsters